From: David Gibson <david@gibson.dropbear.id.au>
To: Stefano Brivio <sbrivio@redhat.com>
Cc: passt-dev@passt.top
Subject: Migration failure across bridge
Date: Tue, 18 Mar 2025 16:21:58 +1100 [thread overview]
Message-ID: <Z9kC9q8ZHoZVChHo@zatzit> (raw)
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Continued investigating the problem with migration failing across a
bridge.
Good news is I've found the problem... or at least one problem. Bad
news is we'll have to change the migration stream format to fix it.
The packets are being dropped in tcp_validate_incoming() due to a
failed PAWS check (skb drop reason "TCP_RFC7323_PAWS"). That in turn
looks to be because we don't preserve TCP timestamp state across the
migration. We preserve _whether_ TCP timestamps are active on the
connection (TCPOPT_TIMESTAMP entry in TCP_REPAIR_OPTIONS), but we
don't preserve the current timestamp values (TCP_TIMESTAMP socket
option). The equivalent CRIU code is
https://github.com/checkpoint-restore/criu/blob/d18912fc88f3dc7bde5fdfa3575691977eb21753/soccr/soccr.c#L266
and
https://github.com/checkpoint-restore/criu/blob/d18912fc88f3dc7bde5fdfa3575691977eb21753/soccr/soccr.c#L572
I'll work on writing a fix tomorrow.
Not yet sure why we didn't hit this with a local migration. I'm
guessing some part of being a local connection means we're bypassing
the PAWS check.
--
David Gibson (he or they) | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you, not the other way
| around.
http://www.ozlabs.org/~dgibson
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next reply other threads:[~2025-03-18 5:22 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-03-18 5:21 David Gibson [this message]
2025-03-18 8:28 ` Migration failure across bridge Stefano Brivio
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